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word-forming element meaning "long, abnormally large, on a large scale," taken into English via Middle French and Medieval Latin from Greek makros "long, large," from PIE root *mak- "long, thin" (cf. Latin macer "lean, thin;" Old Norse magr, Old English mæger "lean, thin;" Greek mekos "length").
macro- or macr-
A prefix meaning "large," as in macromolecule, a large molecule.